1. Field of the Invention
The present invention relates to a resin-sealed power semiconductor device, formed by transfer molding, which is excellent in terms of productivity. The present invention particularly relates to a resin-sealed power semiconductor device, formed by transfer molding, which is small in size and which realizes operation with a large current.
2. Description of the Background Art
A power semiconductor device, such as a power module, operates with a large current and high voltage. For this reason, it is essential to efficiently discharge heat, which is generated by the operation of the power semiconductor device, to the outside of the power semiconductor device.
One of such semiconductor devices is the one that is formed such that: power semiconductor elements are mounted on a substrate that includes a metal plate acting as a heat sink and a wiring pattern formed above the metal plate, the substrate including a ceramic plate interposed as an insulation layer between the wiring pattern and the metal plate; and heat-hardening resin is cast such that silicone gel is positioned between the heat-hardening resin and the substrate (see, e.g., Page 3, FIG. 1 of Japanese Laid-Open Patent Publication No. H08-316357 (hereinafter, referred to as Patent Document 1)).
However, in manufacturing of this conventional power semiconductor device, there are: a process of bonding the external casing, which is formed of thermoplastic resin, to the metal plate; a process of filling and curing the silicone gel; and a process of injecting and curing the heat-hardening resin. Thus, there are a large number of manufacturing processes, causing a prolonged manufacturing time. Accordingly, there is a problem of low productivity.
A power semiconductor device which solves this problem and which is excellent in terms of productivity is the one in which: a lead frame is provided on a metal plate while an insulation layer is interposed between the lead frame and the metal plate; and power semiconductor elements are mounted on the lead frame and sealed with transfer molding resin (see, e.g., Page 3, FIG. 1 of Japanese Laid-Open Patent Publication No. 2001-196495 (hereinafter, referred to as Patent Document 2)).
In the power semiconductor device sealed with transfer molding resin, the outer periphery of the lead frame has portions, each of which is, at one end thereof, connected to a power semiconductor element by a metal wire and each of which acts as an external terminal.
That is, the lead frame, which is provided on the metal plate while the insulation layer is interposed between the lead frame and the metal plate and which has the power semiconductor elements mounted thereon, is sealed with the transfer molding resin together with the power semiconductor elements. However, the other end of each of said portions of the outer periphery of the lead frame protrudes from the resin-sealed portion. The tie bar of the lead frame protruding from the resin-sealed portion is cut away, and each of said portions is used as a separate external terminal.
However, since the sealing with transfer molding resin is performed when the lead frame is sandwiched between upper and lower molds, a protruding direction of each external terminal is in parallel to a surface on which the power semiconductor elements are mounted. In other words, the power semiconductor device sealed with the transfer molding resin has a structure in which the external terminals protrude from peripheral side surfaces of the resin-sealed portion. A bending process is performed on the external terminals for mounting of the power semiconductor device.
In a power semiconductor device, there is a necessity to secure a sufficient spatial insulation distance between external terminals. The conventional power semiconductor device sealed with the transfer molding resin has a structure in which the external terminals protrude from peripheral side surfaces of the resin-sealed portion. If a sufficient insulation distance is to be secured between external terminals, then the power semiconductor device cannot be reduced in size. This causes a problem that a mounting area for the power semiconductor device cannot be reduced.
Moreover, since the bending process is performed on the lead frames that are used as the external terminals, there is a limitation regarding the thickness thereof. For this reason, the amount of current to be applied to the external terminals cannot be increased. Thus, there is a problem that an increase in the current is limited in the power semiconductor device.